• Energy Research

[EN] The current investigation presents a methodology to quantify the error in the greenhouse gas emissions of different electric passenger vehicles when considering the marginal instead of the average CO2 emissions. Both well-to-wheel and life-cycle assessment were carried out. The energy required for the vehicles was calculated by analyzing passenger cars of different segments and different powertrain systems in various driving cycles using detailed vehicle models. Results obtained were compared to the targets set by the European Union, following the current legislation, to highlight a realistic position of the different powertrains (electric, hybrid and combustion engines) in the current paradigm of the transport sector. The approach followed along the study showed vari-ations respecting many previous works, unveiling higher environmental impact -in terms of CO2 -due to electric vehicles usage, although still below the pollution level of internal combustion engine cars, in the case analyzed. In normal conditions, pollution calculated based on marginal emissions turn to be more than the double in the current scenario for the case studied. The standpoint and methodology presented in the present work demon-strate that using average emissions values of the energy generation systems might lead to gross miscalculation of the environmental impact of the future transport sector. Operacion financiada por la Union Europea a traves del Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) de la Comunitat Valenciana 2014-2020 con el objetivo de promover el desarrollo tecnologico, la innovacion y una investigacion de calidad. Proyecto IDIFEDER/2021/53, Equipamiento Para El Estudio Del Fenomeno De Combustion No Controlada En Baterias De Vehiculos Electricos, entidad beneficiaria Universitat Politecnica de Valencia. The authors also acknowledge Agencia Valenciana de la Innovacion for partially supporting this research through DETEBAT-VE project (INN-EST/2021/120).

[EN] Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide range of operating conditions. The high thermal efficiency of RCCI is explained by the combination of a short-duration and well-phased combustion process, which maximizes the fuel-to-work conversion efficiency, together with relatively low combustion temperatures, which increases the specific heat ratio during expansion and reduces thermal gradients for heat transfer losses. The objective of this work is to study the RCCI heat transfer characteristics and compare them to those of the CDC regime. To do this, a single-cylinder light-duty research engine instrumented with 25K-type thermocouples distributed among the cylinder head and cylinder liner is used. First, the influence of some engine settings on the RCCI heat transfer phenomenon is explored by means of parametric sweeps. Later, the RCCI heat transfer characteristics are compared for two different low reactivity fuels (LRF), gasoline and E85. Finally, the heat transfer characteristics of RCCI and CDC combustion regimes are compared at some representative operating points in matched load conditions. The results show that both LRF tested are suitable to be used in RCCI giving similar results in terms of energy usage. Moreover, the ability of RCCI combustion in exploiting the fuel energy to extract useful work is demonstrated, reducing by 13% the heat transfer versus CDC. The authors gratefully acknowledge General Motors Global Research & Development for providing the engine used in this investigation. The authors also acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R).

[EN] The existing political environment and the growing worries about climate change have resulted in the imposition of stringent regulations on traditional propulsion systems reliant on fossil fuels. While new technologies are being investigated to substitute internal combustion engines, their current technological advancement necessitates further development and refinement in order to emerge as a viable alternative to the conventional internal combustion engine. The utilization of hydrogen-powered internal combustion engines has showcased their ca-pacity to rapidly achieve complete decarbonization in the transportation industry. However, these engines continue to encounter limitations regarding their operational range that need to be addressed. The utilization of EGR for controlling combustion instabilities and mitigating NOx formation still has significant limitations in operating at high engine loads, mainly affecting the boost requirements for reaching high power densities. The present work evaluates the potential of substituting the EGR dilution with a water injection system for reaching full load operation on a conventional diesel engine, assuming the minimum modifications required for it to work under H2 combustion. The study is carried out assuming a multi-cylinder engine representing the medium-to high-duty transport sector. The evaluation includes a comparison of the engine performance and emissions obtained when using EGR and water injection at full load, comparing the requirements of the boost system for both strategies to reach power densities of 24 bar of BMEP equivalent to modern diesel applications. The results show that WI allows for significantly reduced boost pressure requirements lowering intake pressure by up to 1 bar, while achieving very similar engine efficiency and a reduction of NOx emissions around 80%, resulting a similar effectiveness compared with EGR. Additionally, WI provides additional prevention against undesired autoignition.

New combustion modes for internal combustion engines represent one of the main fields of investigation for emissions control in transportation Industry. However, the implementation of lean fuel mixture condition and low temperature combustion in real engines is limited by different unsolved practical issues. To achieve an appropriate combustion phasing and cycle-to-cycle control of the process, the laser plasma ignition system arises as a valid alternative to the traditional electrical spark ignition system. This paper proposes a methodology to set-up and optimize a laser induced plasma ignition system that allows ensuring reliability through the quantification of the system effectiveness in the plasma generation and positional stability, in order to reach optimal ignition performance. For this purpose, experimental tests have been carried out in an optical test rig. At first the system has been optimized in an atmospheric environment, based on the statistical analysis of the plasma records taken with a high speed camera to evaluate the induction effectiveness and consequently regulate and control the system settings. The same optimization method has then been applied under engine-like conditions, analyzing the effect of thermodynamic ambient conditions on the plasma induction success and repeatability, which have shown to depend mainly on ambient density. Once optimized for selected engine conditions, the laser plasma induction system has been used to ignite a direct injection Diesel spray, and to compare the evolution of combustion with that of a conventional auto-ignited Diesel spray. The authors acknowledge that this research work has been partly funded by the Government of Spain under the project HiReCo TRA2014-58870-R and grant BES-2015-072119. The equipment used in this work has been partially supported by FEDER project ICTS-2012-06, framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain.

[EN] The European commission is targeting a 15% reduction in CO2 emissions for medium and heavy-duty transportation starting in 2025. Moreover, the next European normative (EU VII) will impose a decrease of 50% for NOx and particulate matter emissions with respect to the current EUVI normative. Meeting these requirements pose a significant challenge to truck and bus manufacturers. Several proposals appeared in the last few years as improve the cabin aerodynamics, decrease the friction losses and improve the powertrain efficiency. The last point involves improving the current combustion systems as well as the transmission and energy management. This work proposes to couple two potential technologies to reduce at the same time the global (CO2) and local pollution (NOx and soot). For this, two truck platforms representative of medium-duty applications (18 ton and 25 ton) are tested using the reactivity controlled compression ignition (RCCI) combustion mode with diesel and gasoline as fuels. In addition, the trucks are electrified to full hybrid technology in a parallel pre-transmission (P2) architecture. A 0D vehicle numerical model is used to evaluate the trucks under four different driving cycles representative of homologation and real driving conditions. The numerical model is validated against on road measurements. The RCCI combustion is modeled by means of a map-based approach with 54 points measured in steady-state conditions. This work presents a complete engine map calibration with measurements up to 350 hp using two combustion modes inside the map (so-called dual-mode dual-fuel). As a baseline, the commercial diesel no-hybrid trucks and the dual-fuel no-hybrid trucks are used. The results show the potential of the dual-mode dual-fuel combustion to achieve ultra-low NOx and soot emissions. In addition, the CO2 target reduction is achieved for several truck platforms and driving conditions due to the hybridization of the driveline. The cycles with large phases of urban driving are the most favorable due to the ability of recovering energy by means of the regenerative braking system and the possibility to avoid large idling phases with respect to the no-hybrid versions. In addition, the decrease of the payload improves the CO2 reduction with respect to the baseline cases. The authors thanks ARAMCO Overseas Company and VOLVO Group Trucks Technology for supporting this research. The authors acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R). The authors also acknowledge the Universitat Polit`ecnica de Val`encia for partially supporting this research through Convocatoria de ayudas a Primeros Proyectos de Investigacion (PAID-06-18).

[EN] Electrified powertrains have been growth in the last few years due to the increase in powertrain efficiency. However, for heavy-duty vehicles the right choice it is not clear. The long-routes and large number of daily kilometres makes that current battery technology it is not prepared to cover the minimum requirements. A mid-term solution is hybrid powertrains. The mix between pure electric range and range extender mode in liquid fuels make perfect to complete a large distance. However, tailpipe pollutant and CO2 emissions are still a disadvantage against pure electric powertrain. This study analyses the potential of hybrid powertrains running in an advanced combustion mode as Intelligent Charge Compression Ignition. Due to the flexibility of the combustion mode different renewable energy fuels are tested: Butanol, Methanol and Biodiesel. The work is focused in urban buses due to the potential of electrified powertrains in this context and the large number of vehicles concentrated in cities. The results show that pure electric bus reduce 54% the CO2 emissions at LCA level. Meanwhile the Intelligent Charge Compression Ignition allows to 32% with one renewable fuel (Diesel-Butanol) and 66% with two renewable fuels (Biodiesel-Methanol) with respect to the non-hybrid diesel reference. Operación financiada por la Unión Europea a través del Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) de la Comunitat Valenciana 2014e2020 con el objetivo de promover el desarrollo tecnológico, la innovación y una investigación de calidad a través del Proyecto IDIFEDER/2020/34 "Equipamiento Para El Desarrollo De Plantas Propulsivas Híbridas Limpias Y Eficientes A Través Del Uso De E-Fuels".

[EN] Soot emissions from diesel engines are an important concern in meeting emissions regulations. Soot emissions are the result of two competing processes: soot formation and soot oxidation. Mechanisms of soot formation are discussed extensively in the literature. Equivalence ratio at lift-off length along with residence time and gas temperature play an important role for soot formation in a diffusion flame. Mixing capability and bulk gas temperature are the most important parameters that influence the in-cylinder soot oxidation process. Normally, research studies of soot formation-oxidation processes have been developed under controlled and not completely representative conditions of engine operation in the field. Therefore, the main objective of this work was to develop a simplified methodology to evaluate in cylinder soot oxidation under 'real' engine conditions. In particular the impact of mixing process and bulk gas temperature on late cycle soot oxidation was evaluated. The experimental measurements were made in a production light-duty diesel engine varying those parameters that have been demonstrated in the literature as the most relevant in soot formation - oxidation processes; injection pressure, ambient density and intake air temperature. To measure soot, two color method was applied by means of an optoelectronic pyrometer. To evaluate the mixing capability a specific "tracer" Apparent Combustion Time (ACT(-1)) based on the experimental heat release and injection parameters was defined. The relationship between both parameters was used to explain the soot oxidation process. (C) 2016 Elsevier Ltd. All rights reserved. The authors acknowledge General Motors Global Research & Development for supporting this research.

In the last two decades engine research has been mainly focused on reducing pollutant emissions. This fact together with growing awareness about the impacts of climate change are leading to an increase in the importance of thermal efficiency over other criteria in the design of internal combustion engines (ICE). In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. In particular, in modern direct-injection diesel engines, the radiation emission from soot particles can constitute a significant component of the efficiency losses. Thus, the main of objective of the current research was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under several representative engine loads and speeds. Moreover, the current research characterized the impact of different engine operating conditions on radiation heat transfer. For this purpose, a combination of theoretical and experimental tools were used. In particular, soot radiation was quantified with a sensor that uses two-color thermometry along with its corresponding simplified radiation model. Experiments were conducted using a 4-cylinder direct-injection light-duty diesel engine fully instrumented with thermocouples. The goal was to calculate the energy balance of the input fuel chemical energy. Results provide a characterization of radiation heat transfer for different engine loads and speeds as well as radiation trends for different engine operating conditions.